Solar control coatings having a layer stack of glass/Si3N4/NiCr/Si3N4 are known, where the metallic NiCr layer is the sole infrared (IR) reflecting layer in the coating. In certain instances, the NiCr layer may be nitrided. Unfortunately, while such layer stacks with NiCr IR reflecting layers provide efficient solar control and are overall good coatings, they sometimes are lacking in terms of: (a) corrosion resistance to acid (e.g., HCl boil); (b) mechanical performance such as scratch resistance; and/or (c) color stability upon heat treatment for tempering, heat bending, or the like (i.e., too high of ΔE* value(s)). For example, a known heat treatable coated article having a layer stack of glass/Si3N4/NiCr/Si3N4 has rather high glass side reflective ΔE* value above 5.0 after heat treatment (HT) at 625 degrees C. for about ten minutes. This high glass side reflective ΔE* value means that the coated article when HT will not approximately match its non-HT counterpart with respect to glass side reflective color after such HT.
Accordingly, there exists a need in the art for a coated article that has improved characteristics with respect to (a), (b) and/or (c) compared to a conventional layer stack of glass/Si3N4/NiCr/Si3N4, but which still is capable of acceptable thermal performance (e.g., blocking a reasonable amount of IR and/or UV radiation) and/or heat treatment. It is a purpose of this invention to fulfill at least one of the above-listed needs, and/or other needs which will become apparent to the skilled artisan once given the following disclosure.
A recent development by the instant inventor, set forth in U.S. patent application Ser. No. 10/338,878, filed Jan. 9, 2003 (hereby incorporated herein by reference), is the use of a layer stack of glass/Si3N4/NbNx/Si3N4, where the NbNx is used as the IR reflecting layer. This layer stack is advantageous with respect to the aforesaid glass/Si3N4/NiCr/Si3N4 layer stack in that coated articles with the NbNx IR reflecting layer realize improved color stability upon heat treatment (i.e., lower ΔE* values) and/or improved durability.
While coated articles having a layer stack of glass/Si3N4/NbNx/Si3N4 represent improvements in the art, they are sometimes lacking with respect to chemical durability. This is because, for example, NbNx suffers damage when exposed to certain chemicals such as alkaline solutions, e.g., upon exposure to a one hour NaOH boil test for measuring durability. In commercial use, pinholes can form in the outer silicon nitride layer thereby exposing the NbNx in certain areas; if it is damaged by alkaline solutions this can lead to durability issues. For example, certain photographs in U.S. patent application Ser. No. 10/370,060, filed Feb. 21, 2003 (hereby incorporated herein by reference) illustrate that Nb and NbNx layers are often damaged by the one hour NaOH boil test (one hour boil in solution including about 0.1 normal NaOH solution—0.4% NaOH mixed with water—at about 195 degrees F.). For the boil test, see ASTM D 1308-87, incorporated herein by reference.
Another recent development is the use of CrNx as an IR reflecting layer in such a layer stack. Unfortunately, while CrNx realizes exceptional chemical durability, its thermal performance is not so good.
Moreover, commonly owned Ser. No. 10/370,060 discloses the use of NbCr and NbCrNx as IR reflecting layers. While NbCr and NbCrNx both realize excellent durability, there is a trade-off between chemical durability and thermal performance in NbCr and NbCrNx based coatings. In particular, alloys with higher Cr content have excellent chemical durability, but better thermal performance is achievable for lower Cr contents. Thus, a compromise has to be made between chemical durability and thermal performance when using coatings which utilize NbCr or NbCrNx IR reflecting layers.
Thus, it will be apparent that there exists a need in the art for coated articles which are capable of achieving acceptable solar control performance, and which are also durable upon exposure to certain chemicals such as acids and/or alkaline solutions (e.g., NaOH boil test).
In certain example embodiments of this invention, a coating or layer system is provided which includes an infrared (IR) reflecting layer comprising niobium zirconium (NbZr) and/or niobium zirconium oxide (NbZrOx) sandwiched between at least a substrate and a dielectric layer. Surprisingly, it has been found that the addition of Zr to Nb causes the resulting coated articles to realize excellent chemical and mechanical durability, and also excellent thermal performance. Moreover, it has surprisingly been found that oxidizing the NbZr (to form NbZrOx) allows even better color stability upon heat treatment (i.e., lower ΔE* value(s)) compared to situations where the NbZr is not oxidized.
In certain example NbZrOx embodiments, it has unexpectedly been found that oxiding (e.g., partial oxiding) is particularly beneficial with respect to lowering ΔE* value(s). For example, in certain example embodiments, it has been found that partial oxiding of the NbZr is particularly beneficial when a particular range of oxygen to metal content in the layer is achieved. For example, the atomic ratio in the layer of oxygen to the total combination of Nb and Zr may be represented, in certain example embodiments, by (Nb+Zr)xOy, where the ratio y/x (i.e., the ratio of oxygen to Nb+Zr) is from 0.00001 to 1.0, even more preferably from 0.03 to 0.20, and still more preferably from 0.05 to 0.15. These oxygen/metal content ranges, for purposes of example only and without limitation unless expressly claimed, have been found to lead to significantly improved ΔE* value(s) combined with good durability.
In certain example non-limiting embodiments, the oxygen (O2) gas flow when sputtering a NbZr target(s) may be from about 0.5 to 6 sccm/kW, more preferably from about 1 to 4 sccm/kW, and most preferably from about 2 to 3 sccm/kW (where kW is a unit of power used in sputtering). These oxygen flows, for purposes of example only and without limitation unless expressly claimed, have been found to lead to significantly improved ΔE* value(s).
For example, the use of NbZrOx in an IR reflecting layer(s) allows the resulting coated article(s) to achieve at least one of: (a) improved corrosion resistance to alkaline solutions such as NaOH (compared to layer stacks of glass/Si3N4/Nb/Si3N4 and glass/Si3N4/NbNx/Si3N4); (b) good thermal performance comparable to that of Nb and NbNx; (c) good mechanical performance such as scratch resistance; and/or (d) good color stability upon heat treatment (e.g., lower ΔE* value(s) than coated articles with layer stacks of glass/Si3N4/NiCr/Si3N4).
Due to its spectral selectivity, niobium zirconium oxide (NbZrOx) provides thermal performance (e.g., IR blocking) similar to or better than NiCr and NbNx, but are surprisingly more durable than both NiCr and NbNx. Moreover, it has surprisingly been found that in certain example instances the use of NbZrOx in/as an IR reflecting layer(s) allows the solar control coating to have significantly improved color stability upon HT (e.g., a lower ΔE* value with a given HT time) than the aforesaid conventional coating where metallic NiCr is used as the IR reflecting layer.
A coated article according to an example embodiment of this invention utilizes such a NbZrOx IR reflecting layer(s) sandwiched between at least a pair of dielectric layers of a material(s) such as silicon nitride or some other suitable dielectric material(s). In certain example embodiments of this invention, the NbZrOx layer is not in contact with any metallic IR reflecting layer (e.g., is not in contact with any Ag or Au layer).
In certain example embodiments of this invention, heat treated (HT) coated articles including a NbZr and/or NbZrOx inclusive IR reflecting layer(s) have a glass side reflective ΔE* value due to heat treatment of no greater than 4.0, more preferably no greater than 3.0, more preferably no greater than 2.5, still more preferably no greater than 2.0, even more preferably no greater than 1.5, and sometimes even no greater than 1.0. For purposes of example, the heat treatment (HT) may be for at least about 5 minutes at a temperature(s) of at least about 580 degrees C. (e.g., ten minutes at about 625 degrees C.).
In certain example embodiments of this invention, the Zr:Nb ratio (atomic %) in the NbZr and/or NbZrOx inclusive IR reflecting layer(s) may be from about 0.001 to 1.0, more preferably from about 0.001 to 0.60, and even more preferably from about 0.004 to 0.50, and most preferably from about 0.05 to 0.2 (e.g., 0.11). For purposes of example only, if a 90/10 Nb/Zr target was used, the Zr:Nb ratio would be about 0.11. In certain example embodiments, the IR reflecting layer comprising NbZr and/or NbZrOx may include from about 0.1 to 60% Zr, more preferably from about 0.1 to 40% Zr, even more preferably from 0.1 to 20%, still more preferably from 0.1 to 15%, more preferably from about 0.4 to 15% Zr, and most preferably from 3 to 12% Zr (atomic %). Nitride gas may also be used so as to at least partially nitride the NbZrOx in certain alternative embodiments of this invention.
Optionally, a protective overcoat of a material such as zirconium oxide may also be provided in certain example embodiments.
In certain example embodiments of this invention, there is provided a coated article including a layer system supported by a substrate, the layer system comprising: a first dielectric layer; a layer comprising an oxide of niobium zirconium (NbZrOx) provided on the substrate over at least the first dielectric layer; and a second dielectric layer provided on the substrate over at least the layer comprising the oxide of niobium zirconium.
In certain other example embodiments of this invention, there is provided a method of making a coated article, the method comprising: sputtering a target comprising niobium and zirconium in an atmosphere including oxygen in order to form a layer comprising an oxide of niobium zirconium supported by a substrate; and sputtering a dielectric layer over at least the layer comprising the oxide of niobium zirconium.